The present invention relates to a method for producing a filtering material of natural origin, suitable for the treatment of liquid effluents, in particular having the ability to retain inside some metals, such as arsenic and chromium, which are notoriously difficult to remove.

Arsenic (As) is a metalloid which is found in three different allotropes forms: yellow, black and gray. Its compounds were used, in the past, as herbicides and insecticides. It is also used in some alloys.

Arsenic and many of its compounds are particularly powerful poisons. Arsenic kills by severely damaging the digestive system and the nervous system, bringing the intoxicated person to death by shock. Compounds containing arsenic are carcinogenic and, in particular, are implicated in the pathogenesis of the bladder cancer, in breast cancer and some cancers of the integumentary system. An extensive scientific literature available in prestigious international journals has now proven that chronic arsenic exposure has multiple effects on health:

- reduces the body's antioxidant defenses, given that arsenic has a high affinity for the sulfhydryl groups of proteins and endogenous metabolites such as glutathione;

- causes oxidative stress directly into the intracellular environment, inactivating several enzymes involved in redox reactions (dehydrogenase, mono-oxygenase, etc.);

- interferes heavily with the endocrine mechanisms regulated by estrogens (hence the suspicion that it may cause breast cancer);

- can directly attack the strands of DNA and cause combined injuries of various kinds.

Inorganic arsenic is absorbed by the gastrointestinal tract and, at the pulmonary level, more than 50% of the dose taken is generally absorbed.

Compounds of organic arsenicals are generally considered not very absorbable and their absorption is relative to their water solubility. Furthermore, these compounds, once absorbed, are easily eliminated with feces and urine; in fact, they are subject to hepatic detoxifying biomethylation, therefore organic arsenicals are less toxic and more easily excreted.

Inorganic arsenic can pass the placenta and cause a fetal damage. It is also considered carcinogenic to the lungs, skin, kidneys and liver, especially in chronic intoxication.

The main route of transport and contamination of arsenic intoxication is water, including that normally used for drinking.

Chromium, especially in its hexavalent form, is also extremely toxic to organisms, as it can alter genetic materials and cause cancer.

In order to eliminate the presence of arsenic and other metals highly hazardous to human health, such as chromium, the present inventors have provided a highly innovative and totally environmentally friendly filtering material capable of retaining at its interior and substantially reducing or even eliminating the metal particles present in polluted liquid effluents, particularly chromium and arsenic.

The object of the present invention is therefore to provide a method for producing a filtering material which ensures health safety but which at the same time can be cost-effective and made with natural materials.

This and other objects are fully achieved according to the invention by a method of producing a filtering material of natural origin having the features defined in the appended independent claim 1.

Further features of the invention are specified in the dependent claims of which the content is to be understood as an integral part of the description which follows.

In short, the invention is based on the idea of creating a filtering material whose raw material is the raw wool waste generated by the shearing of sheep and other animals. The col- lected wool is cleaned and degreased and specially disinfected. The clean and degreased wool is then treated inside a microwave oven at the following conditions:

- Exposure time between 3.5 minutes and 30 minutes; preferably between 7 and 14 minutes.

- The microwave spectrum is usually defined in the frequency range between 1 GHz and 1000 GHz. In the specific case, the process of the present invention operates at a frequency between 1 and 40 GHz, preferably between 1 and 6 GHz.

After the aforementioned treatment, the wool is further treated in a dry heat oven at a temperature ranging from 120 to 250 °C, preferably from 170 to 190 °C for an indicative time of 30 minutes, and finally carded and spun to obtain the filtering material.

The filtering material obtained by the method of the present invention is therefore used for the production of filters.

A further aspect of the present invention is therefore a filtering material obtained by the method described above.

The filtering material obtained by the method of the present invention is particularly effective for the removal of metals, particularly chromium and arsenic, from liquid effluents (for example industrial or civil waste water), since the microwave treatment described above breaks the bonds of the disulfide bridges present in the keratin of the wool, making them become available for the bond with the metals themselves, which are thus retained inside the filtering material.

A further aspect of the present invention is therefore the use of the filtering material obtained with the method of the present invention for the removal of metals, in particular arsenic and/or chromium, from liquid effluents.

According to the studies carried out, the filtering material obtained by the method of the present invention can ensure reductions of chromium and arsenic even of 98%. These results were obtained by using for experimental tests solutions of potassium dichro- mate in water at two different concentrations, i.e. 2 mg/1 and 1 mg/1. The results obtained led to the reduction of hexavalent chromium below the detection limit of the spectropho- tometric method used, i.e. <0.05 mg/1.

Furthermore, a wash test with neutral pH water was carried out to test the restoration of the wool's filtering capacity and the results were excellent. This washing process therefore allows a restoration and re-use of the filter itself.

This practice could be important during the engineering phase of the product as the filter used could be purposely reprocessed and regenerated, thus increasing its value from both an ecological and an economic point of view.

A further advantage of the filtering material described is that it is produced from waste materials of wool processing, which in this way no longer has to be disposed of as special waste. This results in an economic relief for raw wool producers, as well as a considerable economic advantage for filter producers, who can use an extremely low-cost and completely natural material as raw material.